This invention relates to the deposition of thin films onto substrates in single substrate processing chambers, and more particularly, to a vacuum processing system that combines single substrate processing chambers with load lock heating and cooling chambers.
Liquid crystal cells for active-matrix liquid crystal displays (AMLCDs) may comprise two glass substrates or plates between which is sandwiched a layer of liquid crystal material. A thin electrically-conductive film may be formed on the inside face of each plate. A source of power can be connected to the conductive films for changing the orientation of the liquid crystal molecules of the liquid crystal material. Up to 1,000,000 or more different areas of the cells may need to be separately addressed. These different areas are called pixels, and they may be addressed by thin film transistors (TFTs).
A TFT comprises a patterned metal gate over which is deposited a gate dielectric layer and a conductive layer, such as amorphous silicon. Subsequently applied layers, such as doped amorphous silicon, etch stopper silicon nitride, silicon oxide, metal contact layers and the like, may also be deposited over the amorphous silicon thin film. These films may be deposited, for example, by chemical vapor deposition (CVD) or plasma-enhanced chemical vapor deposition (PECVD).
In the semiconductor and flat-panel display industries, as substrates have become larger, permitting a greater number of devices to be formed on a substrate, single substrate processing has largely replaced batch processing of substrates. Single substrate processing permits greater control of the process and allows smaller processing chambers to be used. Additionally, if a problem arises during processing, only a single substrate, rather than a whole batch of substrates, is damaged or lost.
To improve the productivity of a single substrate vacuum processing system, a vacuum processing system has been used that includes a transfer chamber and multiple processing chambers, so that multiple step processes can be performed in different chambers on a single substrate in a vacuum environment. Such a system is shown in U.S. Pat. No. 4,951,601, assigned to applied materials, Inc. and which is hereby incorporated by reference. This system includes a central transfer chamber surrounded by and connected to various process chambers. A robot in the transfer chamber transfers the substrates from one process chamber to another. A vacuum load lock is provided to eliminate the need for evacuating the process chambers prior to each processing step, thereby increasing the throughput of the system.
Glass is a brittle dielectric material that requires slow heating and cooling to avoid cracking or stressing over process temperature ranges which may extend from about room temperature to 450 degrees Centigrade (xc2x0 C.). A significant difference in thermal expansion may occur when heating a large substrate, for example, one which is 550xc3x97650 to 800xc3x971,000 millimeters (mm). This problem may arise due to the failure of the substrate heater elements to provide a uniform temperature across the large dimension of the substrate. Further, the perimeter of the substrate can have more heat loss than its central area, thus lower temperatures than the central area. These temperature nonuniformities lead to thermal stresses. In smaller substrates, for example, substrates 360xc3x97450 mm, the problem is less pronounced but nevertheless evident.
TFTs, as noted, may be fabricated using a CVD or PECVD process. These film deposition processes require relatively high temperatures, on the order of 300 to 450xc2x0 C., and only take seconds to perform, for example, 60 to 240 seconds. The glass substrates useful for AMLCDs are typically quite large, for example, 550xc3x97650 to 800xc3x971000 mm. Thus, it may take several minutes to heat a substrate to the processing temperature and then to cool it back to ambient temperature, after the film deposition process has been completed. If the substrates are being individually heated and cooled, there may be a significant loss of processing time due to heating and cooling delays. Thus, film deposition of individual substrates in several process chambers may result in inefficient operation, unless the possibly long heating and cooling delay times are addressed.
A vacuum processing system having improved throughput that can process large glass substrates in a series of single substrate processing chambers and that solves the heating and cooling delay time problem is disclosed in U.S. Pat. No. 5,512,320, assigned to applied materials, Inc. and which is hereby incorporated by reference. This cluster system comprises a plurality of single substrate processing chambers, a batch-type heating chamber, and batch-type cooling chambers. The chambers are connected to a central transfer chamber. A robot in the transfer chamber can move the substrates among the various chambers in any preselected order. The batch heating and cooling chambers and the single substrate processing chambers provide continuous and rapid substrate processing while allowing adequate time for heating and cooling of glass substrates.
The invention relates to an evacuable chamber of a vacuum processing system in which a substrate to be processed may be heated and a processed substrate cooled. The chamber includes a first section in which the temperature of a substrate to be processed may be increased and a second section in which the temperature of a processed substrate may be decreased. At least one substrate support platform is provided in each of the first and second sections. A barrier may be used to thermally isolate the first and second sections from each other.
The evacuable chamber may function as a load lock chamber to transfer a plurality of substrates to and from a vacuum processing chamber. The load lock chamber may include thermally conductive shelves in the first and second sections. The shelves may include supports to provide a gap between the shelves and the substrates supported thereon.
The invention, in another aspect, relates to a cassette adapted to be positioned in an evacuable load lock chamber. The cassette includes a first section in which a substrate to be processed may be heated and a second section in which a processed substrate may be cooled. Heaters are incorporated into sidewalls of the cassette in the first section, and cooling passageways are incorporated into sidewalls of the cassette in the second section.
The invention, in another aspect, features a method wherein a first substrate is loaded into a heating section of a first vacuum load lock chamber and heated to an elevated temperature. The heated substrate is transferred to a selected process chamber. A second substrate is loaded into a heating section of a second vacuum load lock chamber and also heated to an elevated temperature. After the first substrate has been processed, it is transferred from the selected process chamber to a cooling section of the second load lock chamber. The heated substrate in the heating section of the second load lock chamber is then transferred to the process chamber from which the first substrate was removed. The first substrate is subsequently unloaded from the cooling section of the second load lock chamber.
The invention, in another aspect, also includes loading a substrate onto a platform in a first load lock chamber, increasing the temperature of the platform and positioning the substrate adjacent to another area of increased temperature in the first load lock chamber to heat the substrate. The heated substrate is transferred from the first load lock chamber to a process chamber. After the substrate has been processed, it is transferred to a second load lock chamber and positioned on a platform. The temperature of the platform in the second load lock chamber is decreased and the substrate is positioned adjacent to another area of decreased temperature in the second load lock chamber to cool the substrate.
The method, alternatively, may involve positioning a substrate on a heated platform in the first load lock chamber, processing the substrate and then cooling it by placing it on a cooled platform in the second load lock chamber.
The number of process chambers may equal the number of substrates in the first load lock chamber. A substrate may be inserted into or removed from the first and second load lock chambers on an ambient side thereof in a direction generally perpendicular to a short dimension of the substrate. The substrate may be inserted into and removed from the first and second load lock chambers, and the process chamber on a vacuum side thereof in a direction generally perpendicular to a long dimension of the substrate.
Advantages of the invention may include one or more of the following. The system of the present invention provides an economic and advantageous way of forming high quality thin films on substrates in an efficient and economic manner. The system incorporates a batch-type heating and cooling cassette in a single load lock chamber. The system may also include single substrate heating and cooling chambers providing rapid substrate heating and cooling. The system has a relatively small footprint, and is relatively inexpensive to manufacture and operate.